from Bruce Garrioch at the Ottawa Citizen,

After missing most of last year with post-concussion syndrome, the Senators forward had to be helped off the ice by his teammates after taking a huge hit from blueliner Patrick Sieloff during a training-camp scrimmage on Sunday morning.

MacArthur was down in the corner and was unable to leave without assistance from his teammates. Given his history with concussions, there are concerns about his career. This wasn’t a good sign and MacArthur didn’t return to the scrimmage.

It appeared to be a blindside, ugly hit by Sieloff, a defenceman.

So upset was Senators winger Bobby Ryan with Sieloff, who was acquired from the Calgary Flames in the deal for Alex Chiasson this summer, they dropped the gloves near centre.

continued

Picture of MacArthur being helped off the ice is below...

added 12:32pm, video of the hit is below too....